The utililization of respirators or gas masks to protect against the inhalation of toxic gases is old and well known. Respirators or gas masks having a cartridge or canister filled with activated charcoal have been used to protect the wearer against the inhalation of gases such as vinyl chloride. While these devices provide excellent protection against toxic gases, their protective capabilities diminish with use and eventual permit the passage of gas therethrough unless the filtering material is replaced.
To warn the user of impending exhaustion of the protective capability of the canister or cartridge, various indicating means have been incorporated therein to provide a visual indication of the remaining life. See, for example, U.S. Pat. Nos. 1,537,519, 1,725,893, and 2,961,303. For the most part, the indicators are gas specific; that is, they are sensitive to only a limited number of specific compounds.
Because of recent findings regarding the carcinogenic nature of certain vinyl compounds, in particular vinyl chloride, and the very low threshold limit values of exposure, it is desirable to have available a means of warning of impending exhaustion of the protective capabilities of the respirator or gas mask cartridge or canister. Accordingly, it is an object of the present invention to provide a means for warning of impending canister or cartridge exhaustion. It is a further object of the present invention to provide a detection means that is both accurate and simple for the wearer of the respirator to use.